This invention relates to an information processing system comprising storage device, and more specifically, to remote copying and disaster recovery technology, executed by a remote copy network (hereafter also called an “RCN”) comprising two or more storage devices and two or more network devices.
When failure occurs in a storage device of an information processing system due to electrical power failure, natural disasters or other disasters, operations using the information processing system are halted temporarily, and in the worst case, data stored in the storage device may be lost. In order to avoid such circumstances, there exists technology (hereafter called “remote copying”) through which data stored in storage devices of the information storage system is transferred to and copied in storage devices prepared at a remote location different from the information processing system.
There are two types of remote copying, synchronous remote copying and asynchronous remote copying, and each has advantages and drawbacks. Specifically, in synchronous remote copying, when there is a write request from a computer of the information storage system, after completion of the transfer of data accompanying the write request to a storage device existing at the remote location, a storage device of the information processing system sends a response to the write request to the computer. Hence in synchronous remote copying there is little data loss due to failures, but increased communication line delays between storage devices result in worsened I/O performance between computers and storage devices.
On the other hand, in the asynchronous remote copying described in Japanese Patent Publication No. 3149325, a storage device of an information processing system responds to write requests from computers and transfers data accompanying write requests to the remote location with independent timing. Hence in asynchronous remote copying, even when the distance between storage devices is great, responses can be made to computers prior to the copying of data to the remote location, so that declines in responsiveness to computers tend not to occur. However, in asynchronous remote copying the possibility of data loss is greater than in synchronous remote copying.
In recent years, a multi-hop method which combines synchronous remote copying and asynchronous remote copying has been invented (see Japanese Patent Laid-open No. 2003-122509 and Japanese Patent Laid-open No. 2000-305856).